This invention relates generally to optical pressure detection for detecting the pressure of a fluid, and more particularly to an explosion-proof sensor required in a chemical plant or the like, an optical pressure detection method and an optical pressure sensor which are suited for measuring a fluid pressure in an environment in which high voltage and large current, as produced by a thunderbolt (lightening), develop, a wavelength plate, a polarization selection device and a light distributor used in such an optical pressure sensor, a multipoint-measuring optical sensor system utilizing such a method, and a sensing probe used therein.